Control system and circuits for distributed electrical-power generating stations

ABSTRACT

A system (30) for providing electrical-power to remote communities (34) widely distributed over an extended geographical area (38) includes a generating station (32) located proximate each of the communities, each generating station supplying only that community to which it is proximate. The generating stations are in electronic communication with a central computer (40). Each generating station includes a plurality of generators (54-56). Each of the generators is controlled by a microprocessor based controller (64). Each controller is arranged to operate the generating station cooperatively with the other controllers associated with other generators in the station, and to assume a supervisory role in doing so by a mutual arbitration procedure among the controllers. Each controller is also arranged to monitor important generator operating parameters and to communicate these parameters to the central computer. Any controller may be reprogrammed by instructions communicated from the central computer, and functions of any controller may be overridden by instructions communicated from the central computer. The controllers include novel signal processing circuits (90 and 85) and logic for improved voltage and frequency regulation. The controllers also include novel circuits (92) and logic for monitoring generator fuel consumption and calculating generator fuel-efficiency therefrom.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to automatic control ofelectrical power generators. It relates in particular to a systemincluding a plurality of generators which together provide power for auser group or community, each of the generators including amicrocomputer based controller, and the controllers in electroniccommunication with each other for cooperatively and autonomouslycontrolling the generator group, with an arbitrarily determined one ofthe controllers supervising the operations of the others at any instant,and in electronic communication with a central computer for reportingperformance data thereto and receiving operating instructions therefrom.

DISCUSSION OF BACKGROUND ART

There are remote areas of the world which, however remote they may be,support many small communities. These are typically widely distributedover a large area and are not interconnected by a system of pavedhighways or a distribution system for utilities such as water and power.In such a small community, utilities must be self provided by residentsor businesses or may be derived from a small centralized utility systemlocated in or close to the community. Electricity generators in such acommunity may be of several different types including water, wind anddiesel-engine driven generators.

Diesel-engine driven generators are most common, yet such generatorsoften present a most difficult maintenance problem, requiring intricateadjustments to maintain them at a reasonable operating efficiency orrunning reliably. Further, an electrical generation station generallyrelies on two or more generators. These generators may be of differentcapacity to deal with differing load requirements, which may varyhourly, daily, or seasonally. Typically, at least one back-up generatoris required to maintain power in the event that a primary generator isstopped, for example, through failure, or in order to performmaintenance on the generator.

One significant problem is predicting fuel requirements and maintaininga fuel supply sufficient that power supply continues withoutinterruption. This may result in excessive amounts of fuel being stored.Storing large amounts of fuel requires correspondingly large, long-termcommitment of funds, with attendant interest costs. Storing andtransporting large amounts of fuel may also be environmentallyhazardous, particularly in remote regions which experience extremeweather conditions, for example, Alaska. Storing large amounts of fuelmay mean that a community is not able to take advantage of anyadvantageous fuel price fluctuations.

Another significant problem is maintaining a sufficient quality,consistency, and continuity of power. As many of the above discussedsmall communities now rely on electronic computers, computer-controlleddevices, and digital communications, it is important that a power sourcebe available which provides a consistent narrow range of voltage andfrequency, as such electronic devices may be sensitive to evenrelatively small power fluctuations.

In most circumstances, a small remote community will not have rapidaccess to skilled technical help which may be required to properlymaintain one generator, let alone a system of electrical generators.Transporting such help to a remote location significantly adds to thecost of the help. Maintaining resident skilled personnel in a communityis also expensive, particularly if maintenance is only requiredintermittently.

Microcomputer controlled devices have been devised, which are capable ofautomatically providing basic generator controls such as voltage andspeed (frequency) control. Devices have also been devised which canprovide automatic switching to a stand-by generator in the event ofsudden impending failure of a primary generator, or switching of a loadfrom one generator to another in the event of a load fluctuation. As thepower requirements of small remote communities increase there is anincreasing need for means to provide power to such communities via localgenerating stations which are capable of a high level of autonomouscontrol and self-maintenance, but which may be monitored and controlled,alone or as part of a group, from a remote location.

SUMMARY OF THE INVENTION

The present invention is directed to providing an electrical powergenerator control system which is capable of automatically controllingand operating a plurality of electrical power generators. In oneparticular aspect, the invention is directed to enabling a remotelylocated central operator or computer to monitor and control a system ofautomatically controlled and supervised generating units or stations,each including at least one electrical power generator, and which aredistributed over a geographical region. The generating stations may beautonomously controlled by a microprocessor based controller thereinwhich is programmed for optimally operating the generating station togenerate electrical power; for monitoring selected operating parametersof the electrical power generator; and for transmitting the selectedoperating parameters to the central computer. The generating stationsare also remotely monitorable and controllable from the central computervia an electronic telecommunications link with the microcomputer basedcontroller.

In another aspect of the present invention, one or more of the pluralityof the generating stations may include a plurality of electrical powergenerators which are cooperatively operated to supply a commonelectrical load or demand. Each of the generators in such stationsincludes a microcomputer based controller. Each microcomputer basedcontroller includes means for electronically storing target operationalparameters of the generator connected therewith, and also includes meansfor electronically storing values and logic for operating the generatorassociated therewith, cooperatively with any other generator included inthe generating station, via a similar controller associated with theother generator. The controller also includes means for computing fromthe monitored functions, actual operational parameters of the generatorassociated therewith, and includes means for transmitting signalsrepresenting selected ones of the actual operating status parameters andthe monitored functions to the central computer. The controller furtherincludes means for accepting signals representing generator control andadjustment requests from the central control station, generatinggenerator control and adjustment signals therefrom, and controlling thegenerators as a group using these control and adjustment signals.

The controllers are configured and may be programmed such that, in anygenerating station including more than one generator, one of thecontrollers has a supervisory role in determining how the generatorswill operate cooperatively, and are also programmed and configured suchthat the supervising controller can automatically pass the supervisoryrole to another controller as a result of communicative arbitration.

The above-described configuration and arrangement of controllersprovides that human intervention in the operation of a group ofgenerators is unnecessary except in circumstances such as occurrence ofunanticipated catastrophic events, actual physical replacement of partsor units of the generating station, periodic preventive maintenance, andreplenishment of fuel or lubrication supplies. Controllers may beprogrammed to monitor or compute parameters such as generator efficiency(electrical energy output versus fuel consumed), engine coolant leveland temperature, and engine exhaust temperature, one or more of which,if logged and monitored over a period of time and transmitted to thecentral control station, may provide advanced warning to the centralcontrol station of an impending component or unit failure. Given such awarning, maintenance personnel may be dispatched to the community inwhich the potentially malfunctioning generator is located to rectifywhatever problem is responsible for the impending failure, hopefully,before it occurs.

The above described system provides that many corrective adjustments maybe made to a generator via its associated controller by theabove-discussed control and adjustment signals transmitted from thecentral control station. Preferably it is arranged that the centralcontrol station, by means of these signals, can override any controllerfunction. By way of example these signals may provide that: anygenerator may be remotely enabled or disabled; any protective trippingdevices that have been activated to automatically stop a generator ifcertain predetermined stored operating parameters are exceeded may beremotely reset; generator operating priority may be modified in responseto a permanent change in load profile or to accommodate an extendedtemporary loss of use of one of the generators; and supervisoryresponsibility may be remotely transferred to any particular generatorcontroller.

The controller includes signal processing circuitry for processinggenerator voltage signals before they are used by the controller forvoltage regulation. The circuitry includes means for receiving agenerally sinusoidal positive and negative going first analog signalrepresentative an output voltage of the generator. The circuitry isarranged to convert the first analog signal into a second analog signalhaving only positive going cycles alternate ones of which arerepresentative of the magnitude of alternate positive and negativecycles of said first analog signal. The circuitry is also arranged toconvert the first analog signal into a square-wave pulse signalrepresentative of polarity of the alternate half cycles of the firstanalog signal. The circuitry also includes means for receiving an anlogsignal representative of residual neutral voltage of the generator andcorrecting the received analog generator voltage signal, before it isdigitized, using this signal.

In a preferred voltage control method the controller repeatedly, at afixed time interval, receives above discussed generator output voltageand residual neutral voltage signals, corrects said generator voltagesignal according to said generator residual neutral signal, and providesa corrected generator output voltage signal to a the microcomputer fordigitization and storage. Repeatedly, at a time interval synchronized tothe generator frequency, the stored, digitized corrected, generatoroutput voltage signal, is compared with a predetermined setpoint valueand with a last previously sampled digitized corrected, generator outputvoltage signal. Based on this comparison a voltage error correctionsignal is generated and supplied to a voltage regulator, which isarranged to respond to the signal by generating a generator fieldcurrent drive signal for regulating generator voltage.

As discussed above, the controller may be programmed to compute fuelefficiency of the generator. In one preferred fuel efficiency computingmethod, first and second current pulse signals representing respectivelyfuel flow to and fuel flow from the engine, are received by thecontroller. The current pulse signals have a frequency representative ofvolume fuel flow, and a magnitude representative of fuel temperature.The controller determines from the first and second current pulsesignals, respectively first and second values of fuel volume flow andfirst and second values of fuel temperature. Using the first and secondvalues of fuel volume flow, the first and second values of fueltemperature and from a predetermined standard temperature, the first andsecond fuel volume flows are standardized to the standard temperature.The standardized second fuel volume flow is subtracted from the firststandardized fuel volume flow to determining a fuel consumption value.In response to a signal indicating that the generator has generated 1KWH of electrical energy, the fuel consumption value is mathematicallyinverted, thereby providing a measure of fuel efficiency of electricalenergy generation by the generator.

Fuel flow signals are processed in an electrical circuit, comprisingmeans for receiving a train of current pulses from a fuel flow sensormonitoring the flow of fuel to or from the engine, the current pulsesoccur at a frequency proportional to volume flow of the fuel and have amagnitude representative of temperature of the fuel. The circuitincludes means for converting the current pulses to analog voltagepulses, means for amplifying the analog voltage pulses; and means fordelivering the amplified analog voltage pulses to an analog to digitalconversion device in the microcmputer for digitization.

A system in accordance with the present invention is not limited tointernal combustion engine driven generators for providing electricalpower. A generating station may include generators of different kindsuniquely or in combination, for example, generators driven by hydraulicturbines or windmills. As each generator has its own associatedcontroller, that controller may be programmed with appropriate operatingpowers of the particular generator while still being cooperative withthe other controllers in maintaining a consistent set of electricalparameters for the generated electrical power. A combination ofhydroelectric, wind and diesel generators may be advantageous in areasof heavy rainfall or high winds.

A system in accordance with the present invention is useful not only forsupplying power to widely distributed communities in remote regions, butmay provide a competitive alternative to a monopolistic centralizedpower distribution utility company in more populated areas. A utilitycompany operating a system in accordance with the present invention mayenter the electrical power market without the massive outlay required tobuild a centralized generating plant, which with its associated forestof distribution pylons may be an unwelcome neighbor. In a system inaccordance with the present invention, capacity additions to the systemneed to be done incrementally in response to incremental increases indemand. This would usually prove advantageous for fiscal management ofthe system. Further, a local engine-driven generating station could bearranged to provide waste-heat from the driving engine for buildingheating purposes, and could also provide stand-by power for essentialservices in the event of a power outage in a larger utility system.

In a system in accordance with the present invention each of thegenerating stations may be defined as standalone generating stations, inthat they are not connected in an electrical grid with other suchstations outside of a community in which they are located. They may beindependently, and locally owned, but centrally maintained and managedby a single entity which would provide operating and maintenanceexpertise as well as fuel, thereby affording a relatively small utilitysupplier or user the economies of scale of a large utility company. Agenerating station may be used only on an emergency or stand-by basis bya building or institution which is normally served by a utility companyvia a conventional power distribution network. Such a station could beremotely started and stopped by an operating company for test,evaluation, or adjustment to ensure that it is always in a state ofreadiness.

In yet another aspect of the present invention, a group of such stand-bygenerating units could be located and serve users in several buildingsor institutions distributed throughout a metropolitan area which isusually served by a local grid section of conventional wide-area utilitypower grid. Each of the generators could be arranged to connect with thelocal grid such that, in the event power to the local grid wereinterrupted, the generating stations could be activated and connected tothe grid, thereby providing back-up power not only for the buildings orinstitutions in which they were housed but to other users in themetropolitan area who either did not have a stand-by system or requiredtemporary power until a stand-by system could be started. Means ofmaking such grid connections would be well known to one familiar withthe art to which the present invention pertains. Accordingly, furtherdescription of such grid connections is not presented herein.

The above-discussed advantages of a system in accordance with thepresent invention represent only a fraction of the potential advantages.From this summary description and a detailed description presentedbelow, other advantages of a system for providing electrical power inaccordance with the present invention will be evident to those familiarwith the art to which the present invention pertains

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, schematically illustrate a preferredembodiment of the invention and, together with the general descriptiongiven above and the detailed description of the preferred embodimentgiven below, serve to explain the principles of the invention.

FIG. 1 is a cartographic view schematically illustrating a remotelycontrolled electrical power utility system in accordance with thepresent invention, including a plurality of generating stationsdistributed throughout a wide geographical area, each of the stationsbeing in electronic communication with a central computer.

FIG. 2 is a perspective view schematically illustrating general layoutof an electrical power generating station in accordance with the presentinvention, including a power house, fuel storage tanks and atelecommunications link for communicating with the central computer ofFIG. 1

FIG. 3 is a block diagram schematically illustrating details of a groupof three generators located in the powerhouse of FIG. 2, each of thegenerators including a generator controller in accordance with thepresent invention, the controllers for cooperatively and autonomouslyoperating the generators.

FIG. 4 is a block diagram schematically illustrating details of agenerator in the generating station of FIG. 3, including an engine, analternator, and connections between the alternator, the engine and acontroller.

FIG. 5 is a block diagram schematically illustrating arrangement of amicrocomputer, control-circuits and components and connectionstherebetween in the controller of FIG. 4.

FIG. 6 is a block diagram schematically illustrating arrangement andinterconnection of components of the microcomputer of FIG. 5.

FIG. 7 is a circuit diagram schematically illustrating interconnectionof components of generator-voltage signal processing circuits in thecontroller of FIG. 4.

FIG. 8 is a circuit diagram schematically illustrating interconnectionof components of a fuel-flow meter current-pulse processing circuit inthe controller of FIG. 4.

FIG. 9 is a flow chart schematically illustrating a method of computinga temperature-standardized volume fuel-flow rate from digitizedprocessed signals from the circuit of FIG. 8.

FIG. 10 and FIG. 11 are flow charts schematically illustratingsupervisory functions and decisions of a supervisory one of thegenerator controllers of FIG. 3.

FIGS. 12-15 are pseudo-code diagrams schematically representing softwarearchitecture for setting generator control modes for the microcomputerof FIG. 5.

FIG. 16 and FIG. 17 are pseudo-code diagrams schematically representingsoftware architecture for error correction signal computation forvoltage regulation in the computer of FIG. 5.

FIG. 18 and FIG. 19 are pseudo-code diagrams schematically representingsoftware architecture for error correction signal computation forfrequency regulation in the computer of FIG. 5.

FIG. 20 is a view schematically illustrating one example of a display ofthe central computer of FIG. 1, the display showing a graph of loggedgenerator efficiency versus elapsed time for a generator of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, wherein like components are designated bylike reference numerals, FIG. 1 illustrates a remotely managed utilitysystem 30 in accordance with the present invention. System 30 includes aplurality of generating stations 32, each thereof including at least oneelectrical power generator (not shown). Each generating station 32 issituated proximate a community 34, which may include residential,commercial, and industrial users. Each generating station deliverselectrical power to the community to which it is adjacent via atransmission line (or lines) 36.

Communities 34 are widely distributed over an extended geographical area38, here, whimsically representing a south-western portion of the stateof Alaska. Each generating station 32 is in electronic communication oris electronically linked (represented by broken lines 39) with a centralcomputer 40 which is preferably located in a central managementestablishment in or close to a major metropolitan area 42 of region 38.It is pointed out here that the term "central" as applied to computer 40indicates that the computer is central to the functionality of system30. Clearly, it is not necessary that the computer be geographicallycentrally located, especially when communications are by satellite.

Electronic communication with central computer 40 may be accomplished byvarious means including, for example, hard-wired telephone line,wireless telephone connection, or satellite communications link, aloneor in combination. A general requirement for communication link 39 isthat it is capable of providing two-way, high-speed data transmission,preferably with few interruptions.

It should be noted here that each generating station 32 may be definedas a stand-alone generating station in that it supplies electricity onlyto the community 34 with which it is associated, and is not connectedelectrically, for load sharing purposes, with any other of the remotelylocated generating stations 32. The possibility that two or moregenerating stations adjacent to the same community could be electricallyconnected together in a local electrical grid for supply purposes is notprecluded. The term community, as used herein, may describe a village,hamlet or town or a clustered group of small towns, villages, orhamlets, sufficiently close that electrical transmission from thegenerating station throughout the community can be effected without thetype of high-voltage transmission lines used by centralized utilitiesfor power transmission.

Referring now to FIG. 2, one preferred layout of a generating station 32in accordance with the present invention is illustrated. Here,generating station 32 is arranged to have a total electrical powercapacity of about two-hundred kilowatts (200 KW) and includes threediesel-engine-powered generators (not shown in FIG. 2) housed in agenerator-house or power-house 44. Diesel-fuel tanks 46 preferably havea total fuel capacity of about sixty-thousand gallons of fuel, which issufficient for between about two-hundred-fifty to four-hundred-fiftydays of operation, depending on local demand. A telecommunications unit48 including a dish-antenna 50 provides for communication, via asatellite link, with central computer 40. A perimeter enclosure 52provides security for generating station 32.

Continuing now with reference to FIG. 3, details of a generator group32, and control apparatus therefor, in generating station 32 aredepicted. Here, generator group 52 includes three generators 54, 55, and56. Preferably, but not necessarily, generators 54, 55, and 56 havedifferent power output. Fuel is supplied to the generators, from fueltanks 46, via a manifold 47, by means of a pump (not shown) to a daytank 41. From day tank 41, conduits 45 and 49 carry fuel respectively toand from the engines. In one preferred combination, generators 54, 55,and 56 have power output of about 60.0 KW, 100.0 KW, and 145.0 KWrespectively.

Generators 54, 55, and 56 may be connected, singly or in combination,via breakers 58, to electrical transmission line or load 36. Usually,they are connected in a manner, dependent on the demand of the load,i.e., in a manner in which a generator or combination of generatorssupplies the load most efficiently. Clearly, however, providing morethan one generator ensures that power may continue to be generated,albeit perhaps with less than optimum efficiency, in the event of afailure of one of the generators.

Associated with each of generators 56, 57, and 58 is a microcomputerbased controller 64. Controllers 64 are preferably identicallyconstructed. Each controller is configured and programmed to control thegenerator with which it is associated, to function as a supervisor ofcontrol and operation of generators 54, 55, and 56, cooperatively, as agroup, and to communicate with central computer 40 via a communicationsline 67 and telecommunications unit 48. Each controller 64 is alsoprogrammed to communicate with the other controllers via a hard-wiredcommunications link 66. Each controller preferably has a display 69connected thereto for displaying performance parameters of the generatorwith which it is associated.

Each controller 64 is programmed such that, at any instant, one, andonly one, of the controllers assumes the supervisory function, and theresponsibility of communicating with central computer 40. Assumption ofsupervisory control and communication is determined by a mutualarbitration scheme which is described in detail hereinbelow.

Among functions of each controller 64 are well known functions ofprior-art diesel engine driven generator controllers, such as voltageregulation and speed (frequency) control. In addition, each controller64 is arranged to monitor engine, fuel supply, and generator parameters,and to compute from those parameters other parameters which, alone or incombination, will provide an indication of potential malfunction orfailure of a generator or a component of a generating station, or simplyof generator performance, for example fuel-efficiency.

It is well known that a generator becomes less efficient when loaddemand on the generator falls significantly below the generator'smaximum power-output capability. A number of devices have been devisedwhich are able to control a plurality of generators of differentcapacity, and to select which of these generators is connected to a loaddependent on the magnitude of the load. This is done using predeterminedassumptions of each generator's efficiency as a function of load.Switching from one generator to another is determined by the instantload on the system. Such devices will usually also shut down agenerator, if certain preset conditions are exceeded, to protect thegenerator from potential catastrophic damage. While automaticallyshutting down a generator for this reason is clearly wise, were thecommunity sufficiently remote, however, it may be several days beforewhatever problem triggered the shut-down could be rectified, and powerrestored to the community.

Each controller 64 is arranged to monitor and log parameters,progressive variations in which may be indicative of an impendingmalfunction, and to transmit these parameters and malfunction warningsto central computer 40 where they may be continually monitored. In thisway, a potentially catastrophic malfunction can be anticipated. Skilledpersonnel can be dispatched to rectify conditions threatening themalfunction before it occurs, thereby ensuring that power generationcontinues uninterrupted. Each controller is programmed to log not onlyfunctions of the generator with which it associated but, as asupervisory controller, similar functions of the other generators.

A most important parameter to monitor and log in this regard isgenerator efficiency. Each controller 64 is arranged to actually monitorthose parameters which determine the efficiency of the generatorassociated therewith and compute the efficiency of that generator basedon the monitored parameters. Controller 64 has means to transmit thecomputed parameters and selected ones of the monitored parameters tocentral computer 40, where they can be evaluated and interpreted byskilled personnel. Before continuing with a further detailed descriptionof controller 64, an example of how monitored and computed efficiencyparameters can be used for prediction and control is set forth below.

In a diesel engine driven generator, power generation efficiency can bedefined as electrical energy generated versus energy content of dieselfuel consumed. In controller 64, efficiency is determined by monitoringfuel flow to the generator, return fuel flow from the generator, andaverage power generated. Efficiency is computed by subtracting returnfuel-flow from supply fuel-flow to obtain fuel consumption, and dividingthe average power generated by the fuel consumption to determinegenerator efficiency. Periodic computation and logging of actualefficiency of the generator as a function of power generated, providesan indication of any downward trend in efficiency. A downward trend inefficiency is usually indicative of a progressive maladjustment ormalfunction of the engine.

Flow meters 43 may be installed on each of generators 54, 55, and 56(Shown only on generator 54 in FIG. 3). Alternatively fuel flow sensorsmay be installed only on main fuel supply conduit 45 and return conduit49. Either way, by transmitting fuel flow measurements form sensors 43to computer 50, the total fuel consumed by all generators in generatingstation 42 can be monitored. It is preferably arranged thatinstantaneous fuel capacity and temperature of tanks 46 can be requestedfrom, and monitored by, computer 40 via communications link 39 andconnections 51 between telecommunications unit 48 and the tanks, thusproviding a measure of the rate at which the tanks are emptying.Comparing the rate at which tanks 46 are emptying with the rate at whichfuel is consumed by generators 54, 55, and 56 can provide an indicationthat (if the fuel tanks empty faster than the generators consume fuel)there is a leak in the tank, or in any fuel manifolds or conduitsbetween the tanks and the generators.

Referring now to FIG. 4, a description of signals representing onepreferred set of monitoring and control parameters for a generator ofFIG. 3 (here, generator 56) is presented. These signals are sent fromthe generator to controller 64 and received by the generator fromcontroller 64. The generator comprises an engine 57 and an alternator59. Engine 57 includes coolant (water) inlet and coolant outlet 70 and71 respectively; fuel supply and fuel return lines 72 and 73respectively; an air inlet 74, and an exhaust 75. Represented in FIG. 4,by arrows to or from the generator and alternator, are a preferred setof monitoring or control signals. The signals are designated by name andby a two or three letter code. The letter code is used for designatingthose signals in electronic circuit diagrams discussed hereinbelow todifferentiate them from numerically designated physical components ofthe circuits. Sensors for generating the monitoring signals depicted arewell known to those skilled in the art to which the present inventionpertains. Accordingly, a detailed description and depiction of thesesensors is not presented herein.

Signals which are for alarm and protective purposes only are: (coolant)water temperature (WT) and level (W); fuel supply (FS) and return (FR);oil pressure (OP) and oil temperature (OT); high oil (HO), whichprovides an indication when engine oil is overfilled, and low oil (LO);battery (two lines BV1 and BV2); engine ground (EG) which provides ameasure of the ground potential of those sensors which are attached tothe engine; manifold pressure (MP) which gives an indication of thecondition of a turbo charger (not shown) which is a part of engine 57;and exhaust temperature.

Signals to the engine used for control purposes include fuel on/off(FOD) which is may be used to stop engine 57, and cranking (CKD) whichturns on and off a starter motor (not shown) for starting engine 57. Anactuator control signal (ACD) regulates the speed of the engine via agovernor (not shown) and thus the frequency of voltage generated byalternator 59. These signals are provided by controller 64 of FIG. 3.

Monitoring signals from alternator 59 include voltage of all threephases (VPA, VPB, and VPC); current from all three phases (IPA, IPB, andIPC); and a neutral signal (NTL). Signal NTL provides a measure of anyresidual voltage to ground, which is usually minimal, and is used forcorrecting voltage signals in controller 64. As each kilowatt hour (KWH)is generated by alternator 69, a KWH pulse is initiates a generatorefficiency (KWH per gallon) computation, by the controller, using a fuelconsumption value computed from signals FS and FR. The KWH pulse may besent to controller 64 from alternator 69 or internally generated bycontroller 64.

Breaker status signal BS is used to inform controller 64 whethergenerator 56 is connected to or disconnected from load 36 by breaker 58.If a manual breaker were used and a separate contactor device (notshown) were used to connect and disconnect generator 56, signal BS wouldbe provided by an auxiliary switch (not shown) mounted on the manualbreaker. A line voltage signal VLN is common to all generators ingenerator group 52.

Control signals to alternator 59 include a breaker open/close signal(BOC) which is used by controller 64 to connect or disconnect generator56 to or from load 36, and an alternator field signal which is used toregulate alternator field current and thus output voltage of alternator59.

Referring now to FIG. 5, a description of important components ofcontroller 64 and their interconnection is provided. Controller 64 ispowered via a power supply circuit 83 by a twelve-volt (12 V) or 24.0 Vbattery (not shown) associated with generator 56. Connections betweenthe power supply and components of controller 64 have been omitted forclarity. Controller 64 includes a microcomputer 80, which is discussedin detail hereinbelow, a voltage regulator 82, preferably operating on apulse width modulation principle, a governor controller 84, and relays86 (fuel solenoid relay), 87 (crank drive relay), and 88 (breakeropen/close relay) which provide respectively signals FOD, CKD, and BOCfor controlling engine 57 and for connecting and disconnecting generator56 to and from load 36 (see FIG. 3).

As voltage regulators and governors are described extensively throughoutthe prior art to which the present invention pertains, a detaileddescription of the circuitry of such components is not presented herein.As described herein voltage regulator 82 and governor controller 84 areof relatively simple form and are arranged simply to provide anadjusting signal in response to a received error correcting signalrepresentative of an error to be corrected.

It is pointed out here, however, that the manner in which voltageregulator 82 and governor controller 84 are operated by microcomputer80, and the manner in which data and signals for operating thesecomponents are conditioned and processed by microcomputer 80 and othercomponents of controller 64 to provide such error correcting signals isbelieved to be a novel and important aspect of controller 64. Suchoperation is described in detail hereinbelow.

In this regard, controller 64 includes novel circuits 90 which are usedto process A/C analog voltage signals VPA, VPB, VPC, and VLN before theyare presented to computer. Each circuit 90 receives an input analogvoltage signal for example VPA, representing that phase voltage to beprocessed, and, via a neutral signal processing circuit 85, the NTLsignal representing residual neutral voltage to be compensated for.Circuit 90 corrects the VPA signal according to the NTL signal, and thendivides the corrected signal into an analog portion representinginstantaneous magnitude, and a binary portion representing instantaneouspolarity. The analog and binary portions are delivered separately tomicrocomputer 80. The analog portion is digitized by microcomputer 80 byan internal analog to digital converter, and stored for later use.

It is believed that the above-described analog voltage signal processingstep, provides for more accurate generator voltage control bymicrocomputer 80 and voltage regulator 82 with minimal complexity,whatever the type of voltage regulator used, and whatever the operatingprocedure used by microcomputer 80 for operating the voltage controller.A detailed description of a preferred circuit arrangement for signalprocessing circuits 90 is presented hereinbelow.

Continuing now with reference to FIG. 5, controller 64 includes circuits92 for processing fuel-flow monitoring signals FS and FR. These fuelflow signals are preferably provided by a magnetic, rotary-vaneflow-meter for example a Model 235, manufactured by the FlowscanInstrument Company of Seattle, Wash. which provides a train of currentpulses, the frequency of which is representative of the fuel flow rate.The magnitude of the current pulses is temperature dependent. Aparticularly important aspect of the present invention is the precisedetermination of fuel flow for providing similarly precise computationsof generator efficiency.

In this regard, each of circuits 92 is arranged to convert the incomingcurrent-pulse signal (FS or FR) into an analog voltage pulse signal. Thevoltage pulse signal is digitized and used by microcomputer 80 todetermine the actual volume flow of fuel standardized to a predeterminedambient temperature. This eliminates variability due to periodictemperature changes, which is a particular problem in regions of extremeclimate, or a difference in temperature of supply and return fuel. Thisfuel signal processing aspect of the present invention provides for moreaccurate determination of efficiency trends in a generator performance.A detailed description of preferred circuitry for circuits 92 and amethod of computer processing output signals from the circuits ispresented hereinbelow.

Controller 64 includes a temperature sensor 94 which provides an analogsignal to microcomputer 80 representative of temperature in a housing(not shown) enclosing controller 64. This temperature signal isconsidered important in controller 64 and is used for two purposes. Onepurpose is simply to provide an indication of possible extremetemperature of controller 64 which may interfere with its properfunctioning. The signal is also used by microcomputer 80 for correctingmonitored engine related temperature signals WT, OT and ET which arepreferably provided by bi-metal thermocouples. Such thermocouples arepreferred because they are consistent, and reliable at hightemperatures, for example, exhaust temperatures. However, thermocouplesare relative rather than absolute devices, insofar as they measure thetemperature difference between a warm bimetal junction at a measuringpoint, and a cooler one, connected in a circuit. By locating the coolerjunction right at the controller 64 i.e., making the cool bimetalconnection at the controller, the internal temperature will be almost atthe same temperature as this cool junction, and can be added on to thethermocouple reading to obtain absolute temperature readings at the hot(sensing) junction.

Before proceeding with a description of the layout and functions ofmicrocomputer 80, it should be noted that microcomputer 80 receives bothanalog and binary (two-level, high-low or pulse) signals. In FIG. 5, allanalog signals delivered to microcomputer 80 are designated by theletter "A". These signals require conversion to digital form before theyare can be stored or processed. Any input not so designated is of abinary form.

Referring now to FIG. 6, microcomputer 80 is preferably based on a type80C196KC microcomputer (processor) 100 produced by the Intel Corporationof Santa Clara, Calif. Processor 100 communicates, via a 16-bit widedata bus 102 with a clock/calendar non-volatile, random-access memory(NVRAM) 104; a main NVRAM 106; an erasable, programmable, read-onlymemory (EPROM) 108; and input and output ports 110 and 112 respectively.

Clock/calendar NVRAM 104 provides time and date data for data loggingfunctions which are an important aspect of the present invention. MainNVRAM 106 is used to store all control and set point values necessaryfor operation of generators 54, 55, and 56, and signal processing andcorrecting operations. It is also used to store and log selectedmonitored or computed operating parameters of the generator which it isoperating, and parameters of any generators the operation of which it issupervising. For a system of three generators, as described herein, amemory size of about 128 Kilobytes (128 KB) can store about twelvemonitored or computer parameters over a period of about twenty days.Logging and storage is arranged on a circular basis, such that if datais not received in time, the oldest data will be overwritten with thenewest data.

EPROM 108 stores primarily program instructions for operatingmicrocomputer 80. Microcomputer 80 is self reprogrammable in that it isable to erase the existing program in EPROM 108 and load a new programinto the EPROM whenever controller 64 is not actually running agenerator. This self reprogramming may be performed in response to acommand and new programming instructions transmitted to controller 64from central computer 40, according to a procedure describedhereinbelow.

Leads carrying certain digital or binary signals are connected directlyto processor 100. These are: engine speed ES; a signal (LP) representingline voltage polarity (see FIG. 5); and a signal RCI (see FIG. 5)representing voltage regulator (field) current. All other binary inputsignals shown in FIG. 5 are communicated to processor 100 via input port110 and data bus 102.

Continuing with reference to FIG. 6, processor 100 processesinstructions and data according to a priority scheme which is describedin detail hereinbelow. Those analog signals which have the highestprocessing priority are digitized, and communicated directly toprocessor 100 (which has an internal anlog to digital converter), asrepresented, collectively, by line 114. These signals include themagnitudes of VPA, VPB, VPC, and VLN. All other analog signals aredigitized and communicated to a multiplexer 116 as representedcollectively by line 115. Multiplexer 116 includes a system of buffersand logic for controlling signal flow to processor 100 in accordancewith the priority scheme. Switching and buffering operations ofmultiplexer 116 are controlled by signals from processor 100. Thesignals are communicated to the multiplexer via data bus 102 output port112, and a connection 120 between the output port and the multiplexer.

As analog-to-digital and digital-to-analog conversion devices are wellknown to those skilled in the art to which the present inventionpertains, placement of such devices will be evident to such skilledpersons from the written description of important elements of FIG. 6.Accordingly, a representation of such devices has been omitted from FIG.6 for clarity. Similarly, buffering and multiplexing logic arrangementsare also well known to those skilled in the art to which the presentinvention pertains. Accordingly a detailed description of a circuitarrangement for multiplexer 116 is not presented herein. Suitablecircuit arrangements for multiplexer 116 will be evident to such skilledpersons from a detailed description of a preferred signal processingpriority scheme presented hereinbelow.

A connection 122 via communications lines 66 and 67 (see FIG. 3)provides for two-way communications directly between processor 100, likeprocessors in the other controllers 64 of generator group 52, andtelecommunications unit 48. Control signals RCO and ACO for controllingvoltage regulator 82 and governor controller 84 (see FIG. 5) aretransmitted directly thereto from processor 100.

Control signals for operating relays 86, 87 and 88 are transmitted fromprocessor 100, via data bus 102, output port 112 attached thereto, and athree-line connection represented by line 126, to a "watchdog" circuit128. Watchdog circuit is controlled by signals transmitted thereto fromprocessor 100 via line 130 and simply provides that the relays will notenergize unless the controller is operating in a normal acceptablefashion. Lines 186, 187, and 188 connect the watchdog circuit to thecorresponding relays.

As discussed above, voltage control accuracy is considered veryimportant in a controller in accordance with the present invention.Accordingly, specific circuitry has been included in controller 64 whichcontributes, together with other aspects of the controller, to providingsuch accuracy. In controller 64, generator phase-voltage signalprocessing circuits 90 address two specific problems. One of theseproblems is the generally recognized difficulty of accurately digitizinga positive and negative going AC signal in a conventional ADC device.The other problem is inaccuracies in measured voltage due to variationsbetween the neutral line and ground.

FIG. 7 depicts circuitry which provides VPA, VPB, VPC, and VLN signalprocessing circuits 90 depicted schematically in the form ofinterconnect blocks in FIG. 5. Circuits 90 are identical. Accordingly,the description presented below for an upper one of the circuits (forsignal VPA) suffices for the remaining three circuits. All four circuitsare depicted, however, for the purpose of illustrating the manner inwhich neutral signal (NTL) correction is applied to the circuits.

The VPA signal is applied to an input pin 200 of circuit 90, the inputVPA signal having a positive and negative going, generally sinusoidalform as illustrated by symbol 202. Resistor R1 preferably havingresistance of about two Megohms (2 MΩ) converts the voltage signal intoa current signal. Capacitor C1 and resistor R3 provide two paths forthis current. In one path, high frequency noise is diverted away fromthe circuit by capacitor C1. Capacitor C1 has a value of abouttwo-hundred-seventy picofarads (270 pF). In another path, the lowestfrequency of interest is supplied to the circuit via resistor R3 whichhas a value of four-hundred-seventy Kilohms (470 KΩ).

Neutral voltage signal NTL input at pin 204 is converted to a currentsignal by resistor R4. which preferably has a value of about 2 MΩ. Theconverted signal is then inverted and restored to a voltage signal by anoperational amplifier 206 and a resistor R5 preferably having a value ofabout 261 KΩ. Comparator 206 is preferably a type TL084 amplifiermanufactured by Texas Instruments Inc. Components R4, R12, R5, C2, andcomparator 206 constitute neutral signal processing circuit 85 of FIG.5.

Diodes D1 and D2, amplifier 208 and resistors R7 and R9 form acurrent-mode precision full-wave rectifier. Resistors R7 and R9preferably have values of 20 KΩ and 22 KΩ respectively, and amplifier208 is preferably a type TL084 amplifier. The voltage output ofcomparator 206, representative of NTL inverted, is converted back into acurrent signal by R6 and added to the current converted VPA signal atthe input to the rectifier. The result, which is VPA-NTL, is thenrectified and the resultant signal is delivered to output pin 209 in theform indicated by symbol 210, which has only positive going cycles.Alternate ones of these cycles represent the magnitude of successivepositive and negative going cycles of the original VPA-VNL signal.

The positive input side of a comparator 212 is connected to the positiveinput side of amplifier 208 thereby detecting only positive going cyclesinput to amplifier 208. Comparator 212 is preferably a type LM339manufactured by National Semiconductor Inc. A small voltage of about 50millivolts (mV) is applied to the negative side of comparator 212. Thissmall voltage ensures that a zero input on the positive input tocomparator 212, as during negative going signal cycles, will produce thecorrect low output from comparator 212. A square-wave pulse signalindicated by symbol 214 is delivered to output pin 216. This signal isused by microcomputer 80 to identify the polarity of the alternatecycles of signal 210.

The following resistor values or ratios are important to the properfunctioning of circuit 90. The input circuitry of R1, C1, and R3 mustmatch the NTL circuitry of R4, C2, and R12, and the values of R5 and R6must match. This ensures that the NTL and VPA currents supplied todiodes D1 and D2 are in similar ratios. R7 should be equal to thecalculated resistance of R6 and R9 in parallel to obtain symmetry of thepositive and negative cycles on the output of amplifier 208.

Turning now to FIG. 8, components and interconnections of a fuel-flowsignal processing circuit 92 are illustrated. Circuit 92 is designed toconvert current pulses draining to ground at FS into voltage pulsessuitable for analog-digital-conversion. A fuel flow signal, here FS, isinput into circuit 92 via input pin 220. During the "on" portion of theFS pulse, current flowing to FS is supplied across R22, which has avalue of 1 KΩ. This causes voltage drop to a level below the 5 V supplyvoltage. The drop below 5 V is amplified by amplifier 222, preferably oftype TL084, by a voltage ratio equal to 5.91 that is set by resistorsR26, (having a value of 49 KΩ) and R24 (having a value of 10 KΩ). Whenthe FS input pulse is "off", all voltages at the inputs and output ofamplifier 222 change to the 5 volt level. These two voltage levels aredelivered as a string of voltage pulses via output pin 224 tomicrocomputer 44. The maximum value at pin 224 is close to 5 V, and theminimum value is about 3 to 4 volts.

A preferred method for processing these signals, and for using theprocessed signals to determine generator efficiency is set forth belowwith reference to FIG. 9, wherein the method is depicted schematicallyin flow chart form in flow chart form.

FIG. 9 shows that fuel supply FS and fuel return FR are separatelycalculated and temperature compensated to a standard temperature, i.e.,to a specific density at the standard temperature, and the resultssubtracted to obtain fuel flow. The fuel flow is in turn processed,using above-described KWH pulse information, to provide a measure ofefficiency of generator 56. This calculation and compensation isdescribed here in terms of fuel supply signal FS.

There are three asynchronous elements of the efficiency calculationprocess. These are: a sampling of FS and FR signals which is done on afixed time interval basis; a pulse frequency and magnitude calculationwhich is synchronized to the pulse frequency; and an efficiencycalculation which is synchronized to KWH production by the generator.

Voltage pulses output from circuit 92 after conversion from currentpulses (box 230) have a frequency between about thirty Hertz (30 Hz) and300 Hz and a form which may be described as an asymmetric square form.The pulses are digitized for processing by microcomputer 80 (box 231).Microcomputer 80 is programmed to sample the digitized signals atintervals of about one millisecond, and to determine, from the sampling,the highest value HV of voltage (box 232) and the lowest value LV ofvoltage (box 233) input from circuit 92. The millisecond sampling rateis sufficiently fast that the HV and LV values accurately represent thepeak and trough of a pulse.

The lowest value LV is subtracted from the highest value HV (box 234)and the difference is multiplied by a stored calibration factor todetermine fuel temperature (box 235). An average or mid-point value((HV+LV)/2) is computed (box 237) and compared with incoming pulses inbox 236 to determine when the input voltage from circuit 92 has crossedthe computed mid-point. Mid-point crossings are counted (box 238), andthe count frequency is to determine a flow velocity. The flow velocityand temperature are then used to determine the standardized fuel flow(box 240). The standardized fuel return flow is subtracted from thestandardized fuel supply flow to determine fuel consumption (box 242).

After every temperature determination (box 234), the recorded value ofHV is incrementally decreased and the recorded value of LV isincrementally increased by an amount that will track slow decreases inHV or slow increases in LV. If this were not done the maximum HV andminimum LV recorded would be held indefinitely, in which case no furthertemperature changes would ever be tracked. An incremental increase anddecease rate that will reset HV and LV over an interval from twentyseconds to a few minutes is preferred.

On receipt of a KWP pulse representing generation of a KWH increment(box 244), the amount of fuel consumed since the last KWP pulse wasreceived is calculated (box 246). The inverse of the fuel consumedprovides a measure of generator efficiency in terms of Kilowatt Hoursper gallon (KWH/gal).

It is pointed out here that while all controllers can execute the abovedescribed procedure and compute efficiency of individual generators, ina preferred embodiment of the present invention there is only oneefficiency monitoring point per generator group. This is in the interestof economy (fuel flow sensors are expensive) and reducing programmingcomplexity. The efficiency computation task is assigned to onecontroller 64 only, and is performed by that controller even if thegenerator it is controlling is not on-line or operating.

The above presented detailed description of a multiple generator controland management system in accordance with the present invention, isdirected primarily to hardware aspects of the invention. Set forth belowis a description of programming aspects of microcomputer 80 for carryingout the control and monitoring tasks of the present invention.

Programming for microcomputer 80 consists of a series of routines orcode blocks which are carried out asynchronously, according to apredetermined priority scheme which can be varied only by reprogrammingmicrocomputer 80. The priority scheme groups control, monitoring,logging and communication routines into four priority levels. Certain ofthe routines will be familiar to those skilled in the art to which thepresent invention pertains and are be described hereinbelow briefly ormentioned only by title. Those which are considered particularlyimportant are described in detail with supporting illustration whereappropriate.

The highest or fourth priority level includes eight routines. Each ofthe routines in this level, once initiated, are carried to completion,without interruption for any reason. These routines are: communicationstransmitting a byte; communications receiving a byte; initializingexecution of a new program remotely loaded; governor actuator drive andcurrent sampling; field drive timing for the voltage regulator;generator voltage zero crossing detection; and line frequency zerocrossing detection.

The next (third) priority level is directed to power and efficiencycalculation and includes code for sampling all voltages and currents;calculating fuel flow and fuel consumption using the above discussedtemperature compensation scheme; and, from this sampling andcalculation, calculating power, reactive power, and the differencebetween line and generator voltages.

This third-level sampling is performed about 1000 times per second butthe sampling interval is not a fixed interval. The actual interval is apredetermined fraction, preferably one-forty-eighth, of a frequencycycle, and is phase and frequency locked to the alternator outputfrequency by monitoring frequency and timing of VPA polaritytransitions.

The second level routines are interuptable and are directed primarily togenerator control functions. Second level routines include checksagainst stored test or preset values for protective trips and alarms.Several timed controlled functions are executed in this level. This issimplified by consistently spaced execution. The routines include checksfor: high and low alternator voltage and frequency; high internaltemperature of controller 64; low oil level and pressure; high oillevel; high water temperature; high exhaust temperature; failure tomaintain minimum power; loss of synchronization while running; failureto start; and a remote request for a trip (shut down). A battery voltagecheck is made only for an alarm level.

Also executed at the second priority are routines for generator control;governor (frequency) control; and voltage regulator control. A detaileddescription of these routines is presented hereinafter.

At the first or lowest level are performed background routines which arenot time-critical. These include: analysis of data packages receivedfrom either central computer 40 or from a controller 64 which may hasassumed a supervisory function; organization of data packages fortransmission; read-in of non-time critical analog variables, such as;management of reprogrammability; calculation of generator (fuel)efficiency; and all data retrieval and logging.

Before presenting a description of any of the above discussed generatorcontrol routines in detail, it is important to describe supervisoryfunctions of a controller 64 and the scheme by which a controller 64assumes a supervisory role. As discussed above, an important aspect ofthe present invention is that one, and only one, of controllers in agenerator group assumes supervisory control of cooperative operation ofthe generator group at any instant. Each controller being preferablyidentically constructed and containing an identical program, thesupervisory role can be assumed by a controller of any generator that iscurrently connected to load 36. Only the supervisory controller can sendand receive communications to central controller 40.

A supervisory controller, at intervals of about one minute, sends out acommand to all other controllers to set control modes of thosecontrollers and voltage and frequency setpoint values for voltage andfrequency control. The other controllers reply to the command bytransmitting to the supervisory controller their current operating mode,and the alarm and trip status, power and reactive power and averagevoltage of the generator with which they are associated.

Initial assumption of the supervisory role is done by a random selectionprocess. In one preferred such process, after initial power up, eachcontroller waits for a period of time greater than sixty seconds but notless than one-hundred-twenty-five seconds before assuming thesupervisory function. Each controller 64 is provided with a uniqueserial number from 1 to 65535. This number is stored in microcomputer80. The waiting time is calculated by microcomputer 80 adding sixtyseconds to the controller's serial number expressed in milliseconds.Hence, immediately after an initial system start-up with all controllersenergized together, and no controller having yet a supervisory role,that role will usually be assumed by the controller having the lowestserial number. This scheme also provides that two controllers will notusually attempt to assume control simultaneously.

Immediately after assuming a supervisory role, the supervisorycontroller 64 broadcasts the above discussed command which may bedefined as a "who's there" message over communications line 66 to allother controllers 64. On receipt of the "who's there" message, the othercontrollers will reset the control assuming routine, operate theirprograms in the monitoring mode only, and report their operatingparameters and status to the supervisory controller as discussed above.Subsequently, supervisory commands will be sent at least every minute.If no supervisory command is heard by a controller 64 for a minute plusits serial number times milliseconds, then that controller will attemptto take over supervisory responsibilities. In this manner, supervisorycontrol is re-established even if the supervising controller isincapacitated without warning. The other controllers will respond withdata packages after waiting a time period based on their serial number.One preferred method is to compute the modulus of the serial numberdivided by 2000 and use the result expressed in milliseconds as thewaiting period.

The supervisory controller will retain the supervisory role until thegenerator which it is controlling is taken off line or shut down, eitherby the controller or by a request received from central computer 40.Once a controller 64 has assumed supervisory control, that controllerassumes the responsibility for starting and stopping generators under avariety of circumstances; distributing load demand optimally amongavailable generators; responding to alarm and trip messages generated byany of the controllers, including itself, time-keeping, fine frequencyadjustments, fine voltage adjustments, and communicating viatelecommunications link 39 with central computer 40.

Regarding starting and stopping functions, and configuring generatorsfor load distribution in response to instant demand, an illustration ofcertain of these functions is provided in a decision tree or flow-chartform in FIG. 10 and FIG. 11. Flow charts depicted in FIGS. 10 and 11represent a program cycle of microcomputer 80 which occurs constantly,approximately ten times per second, to determine if a currentlyoperating generator configuration should be changed, i.e., generatorseither removed or added to optimally accommodate an increasing ordecreasing load, and implements such a change.

A target configuration is referred to in FIGS. 10 and 11. This targetconfiguration is a configuration which provides an operator determinedcompromise between efficiency of generation and generator stops and alsoprovides some margin to accommodate some load increase without aconfiguration change being required. FIG. 10 depicts a first programsection which determines whether a change of target configuration isnecessary. FIG. 11 depicts a second (operational) program section(starting at point A) which implements a configuration change ifnecessary.

Referring to FIG. 10, a check is made (box 250) to determine if anygenerators currently on-line are operating above a preprogrammedmaximum, continuous-running output. Generators which have a trip pendingare regarded as having zero capacity. If the answer is yes, the programnext checks to determine if all generators are above their programmedmaximum output or if any have a trip pending (box 251). If the answer isno, the program proceeds to the beginning of the operational section(box 252). If the answer is yes, the program next determines (box 253)the smallest capacity configuration of available generators capable ofproviding the current load plus an operator determined constant based onabove-discussed target configuration compromise criteria. Generatorswhich are out of service, tripped or have pending trips are counted ashaving zero capacity for purposes of this determination. The programnext increments an increasing load change configuration timer (ILCCT)variable (box 254). Next, the program determines if the incrementedILCCT has reached an operator preset delay time, or if any thegenerators have reached a load limit. If the answer is no, the programproceeds to the operational section (box 252). If the answer is yes theILCCT timer variable is reset (box 256) and the program proceeds (box257) to set the configuration determined (proposed) in box 253 as thecurrent (new) target configuration (box 254), and then proceeds to theoperational section (box 252).

The foregoing description has been concerned with how a supervisorycontroller 64 decides how to respond to increasing load. Continuing withreference to FIG. 10, the following description describes how asupervisory controller 64 decides how to respond to decreasing load.

Returning to box 250, if it is determined that no generators areoperating above their preprogrammed maximum output, the program proceedsto determine (box 258) if there is an available generator configurationwhich is lower in maximum capacity than the current configuration but isstill greater than the current load requirement. If the answer is no,the program proceeds (box 259) to reset an decreasing-load,configuration-change-threshold accumulator variable (DLCCT), the purposeof which is discussed below, and then proceeds (box 252) to theoperational section.

If (box 258) it is determined that a different generator configurationis available, the program proceeds to calculate (box 260) a currentfractional capacity difference between the proposed configurationcapacity and the current load and accumulates this in the abovediscussed variable DLCCT. The program next determines (box 261) if theaccumulated DLCCT is greater than an operator determined constant (basedon above-discussed target configuration compromise criteria). If theanswer is no, the program proceeds to the operational section (box 252).If the answer is yes the program proceeds (box 257) to set the proposedgenerator configuration as a (new) current target configuration.

Referring now to FIG. 11 the above discussed operational program sectionis described. This section of program is responsible for implementing aconfiguration change if one has been proposed in the previous section.

The program first decides (box 262) if all generators required by thetarget configuration are on-line or in the process of coming on line. Ifthe answer is no, the program initiates (box 263) a start sequence forgenerators which have not already started or are not on-line. If theanswer is yes the program proceeds to determine (box 264) if there areany generators on-line which are not required by the targetconfiguration. If the answer is yes a stop sequence for all suchgenerators is initiated (box 265).

Whether or not any start or stop sequences have been initiated, theprogram proceeds to adjust target setpoint voltage of generators by theamount the actual line voltage varies from an exact nominal value (box266). Next (box 267) the program adjusts the target line frequency by anamount up to but not greater than 0.1 Hz off of a nominal 60 Hz value.This is based on an accumulated "time-keeping" error which is based onthe difference between one time period determined by counting actualfrequency cycles as being exactly one sixtieth of a second and anothertime period determined over the counting period by internal clock (Q) ofmicrocomputer 80. It is arranged that a ten second error in time willgenerate the maximum 0.1 Hz deviation. Larger errors do not cause largerdeviations but are stored for eventual correction. The frequencysetpoints of on-line generators are then adjusted (box 268) by an amountthat actual line frequency deviates from setpoint frequency.

Next, (box 269) for all on-line generators, the program reviews the Wattloading of individual generators and adjusts the frequency setpoints ofthose generators up or down by an amount equal to the averaged loadingof all generators and the corresponding individual generator's loading.Loading, in this case, refers to a loading determined as a percentage ofthe generators' maximum continuous-running capacity. This frequencysetpoint adjustment is restricted to adjust individual setpoints by nomore than 0.1 Hz, as loading will normally share equally betweengenerators provided their frequency setpoints are essentially identical.

The program next reviews (box 270), for all on-line generators, the VARloading of individual generators and adjusts the voltage setpoints ofthose generators up or down by an amount equal to the averaged(percentage of maximum) loading of all generators and the correspondingindividual generator's (percentage of maximum) loading. This voltagesetpoint adjustment is restricted to adjust individual setpoints by nomore than 5 percent, as VAR loading will normally share equally betweengenerators provided their voltage setpoints are essentially identical.

Finally (box 271) if a configuration change has been initiated theappropriate supervisory start or stop commands are sent immediately togenerators affected by the change. Also whether or not there has been aconfiguration change the program sends every minute at least one set ofvoltage and frequency adjustment commands. This may be done at morefrequent intervals if deviations in voltage and frequency are severe.

It should be noted here that a supervisory controller, 64 in addition toreconfiguring and starting and stopping generators automatically, asdiscussed above, will do so in response to a remote or local signal orcommand received along communications line 66. The local signal istypically generated by a manual start or stop button (not shown). Theremote signal would usually be transmitted from central computer 40.

To ensure that voltage regulators of on-line generators do not fightunnecessarily for control of a generator configuration system voltage,individual voltage regulators are arranged to permit generator voltageto drift up or down slightly in response to reactive power flow. As theline voltage changes as a result of this action, controller 64 adjuststhe voltage regulators of all other on-line generators to compensate(boxes 272 and 274). Similarly, to ensure that governors of on-linegenerators do not fight unnecessarily for control of a generatorconfiguration system frequency, individual governors regulators arearranged to permit generator frequency to drift up or down slightly inresponse to KW flow. If the line frequency changes, controller 64adjusts the governors of all other on-line generators to compensate(boxes 276 and 278).

The switching, starting, and stopping operations described above providethat load is balanced among running generators as a percentage ofgenerator output capability and will be executed by controller 64,except in the following circumstances. When two or more generators arerunning and one is to be arbitrarily shut down, for example, forinspection, the supervisory controller 64 will transfer that generator'sload to the other generator or generators. When a generator has justbeen connected to load 36, the supervisory controller will graduallyincrease that generators load to match the other generators.

Finally, but not exhaustively, when an engine provides an alarm warningas a result of a monitored parameter reaching a preset alarm level,controller 64 will start one or more other generators and transfer thealarm-providing generator's load to those generators. The controllerwill communicate the alarm and the cause of the alarm with centralcomputer 40, and will lock-out the alarm-providing generator fromfurther operation unless it is required to provide power continuity. Ifa generator has been tripped, controller 64 will report the time andcause of the trip to central controller 40, and will lock that generatorout of further operations until the cause of the trip has beenrectified.

Continuing now to with reference to FIG. 12, generator controloperations of a supervisory controller 64 are next described. Generatorcontrol code is executed by microcomputer 80 of controller 64 every 10milliseconds. Each generator is controlled by the code according to oneof eleven modes or code sequences of operation. These modes are:tripped; out-of-service; ready-to-start; cranking, i.e., attempting tostart; cranking wait, i.e., when a generator start has been attempted,has failed after a preset crank count, and is waiting to crank again;coming-up to speed, i.e., when a generator has been successfully startedand is being brought into a condition to connect to load 36; stand-alonerunning i.e., when a generator is running at a nominal speed not yetsynchronized or connected to load 36; synchronizing, i.e., whengenerator voltage polarity and phase are being synchronized with loadpolarity and phase; on-line; unloading, i.e., when a generator istransferring its load prior to shut down; and cool-down.

If an immediate type trip is indicated, the appropriate generatorscontrol mode is set to "tripped" (box 290). If the generator is notalready tripped, but a trip is signalled as pending, the controller willset the generators control mode to "cool-down" after a brief presetdelay, the delay being required to give another generator a chance tostart (box 292).

Every ten milliseconds the supervisory controller will select one of thefollowing sections of coded instructions to execute (box 294). If thecontrol mode is "tripped" (box 296), the controller ensures that relays86, 87, and 88 (see FIG. 5) are off; and, if either the associatedbreaker 58 (see FIG. 3) is open, a manual stop command has beenreceived, or a trip code has been cleared, the control mode will be setto "out-of service".

In the "out-of-service mode" (box 298), the controller ensures thatrelays 86, 87, and 88 are off, clears trip codes; and, if the associatedbreaker 58 is closed, changes the control mode to "ready-to-start". Inthe "ready to start mode" (box 300), the controller ensures that relays86, 87, and 88 are off, initializes (clears) a number of cranks count tozero, and clears all alarm codes. If the associated breaker 58 isopened, the control mode is changed to "out-of service". If either alocal or remote start signal is received, the control mode is set to"cranking".

In the "cranking" control mode (box 302), the controller turns on fuelsolenoid and crank relays 86 and 87. Engine 57 (see FIG. 4) is thencranked until the engine starts and reaches a preset threshold speed, ora preset crank time elapses, whichever occurs first. If the preset cranktime elapses, then crank count is incremented (indicating that one starthas been attempted) and the control mode is set to "cranking wait". Ifengine 57 starts, and the speed exceeds the preset threshold, thecontrol mode is switched to "coming-up-to-speed". Otherwise, the controlmode is set to "out-of-service" if either breaker 58 is opened, or astop signal is received.

Continuing now with reference to FIG. 13, in the "cranking wait" mode(box 304), microcomputer 80 turns on only fuel solenoid relay 86. Aftera preset inter-crank time has elapsed, the crank count is compared to apreset maximum permissible number of cranks. If the crank count is equalto the maximum number of cranks, the control mode returns to "tripped",as engine 57 has failed to start after this maximum permissible numberof cranks. If the maximum number of cranks has not been reached, thecontrol mode is returned to "cranking". If the engine starts and thepreset speed threshold is exceeded, control shifts to the"coming-up-to-speed" mode. Otherwise, the control mode is switched to"out-of-service" if either breaker 58 is opened, or a remote or localstop signal is received.

In the "coming-up-to-speed" mode (box 306), microcomputer 80 turns ononly fuel solenoid relay 86. If a preset nominal (not yet synchronized)running speed is reached, control is switched to the "stand-alonerunning" mode. Otherwise, the control mode is switched to"out-of-service" if either breaker 58 is opened, or a remote or localstop signal is received.

In the "stand-alone running" mode (box 308), microcomputer 80 turns ononly fuel solenoid relay 86. If a "syncing only" flag is received,indicating that the generator voltage polarity and frequency are to besynchronized with the line or load voltage and frequency prior toconnecting the generator to the load, then control mode is immediatelychanged to "synchronizing". Otherwise, the control mode is switched to"cool-down" if either breaker 58 is opened, or a local stop signal isreceived; switched to "synchronizing" if allowed and a local start orremote signal is received; or switched to "cool-down" if synchronizingis allowed, and this mode is run longer than a preset maximum time.

Continuing with reference to FIG. 14, in the "synchronizing" mode (box310) microcomputer 80 turns on only fuel solenoid relay 86. If thecomputer operates in this mode for longer than a preset maximum allowedtime, the control mode is set to tripped on failure to synchronize. Ifline 36 is "dead", and connection to a dead line is allowed, control isswitched to the "on-line" mode after a preset delay.

If the instantaneous voltage difference between the output of alternator59 and line 36 (line 36 is "live") is less than a preset threshold, thena slip count is incremented. If it is greater than the preset threshold,the slip count is reset. When the slip count is above a presetthreshold, the relative frequency difference of alternator 59 and line36 is guaranteed low enough for synchronization. This is one of threerequired criteria for synchronizing. If the instantaneous difference involtage magnitude between the alternator output and the line is belowthe preset threshold, the second of the three required criteria forsynchronizing is met. If the phase angle between the alternator waveformand the line waveform is less than a preset maximum, then the relativephase is sufficiently close for synchronization. This is the third andlast requirement for synchronization.

If all three required criteria are met, control mode is switched to"on-line". Otherwise the control mode is switched to "cool-down" ifeither breaker 58 is opened, (disconnecting the generator from theline), or a remote or local stop signal is received In the "on-line"mode (box 312), microcomputer 80 turns on fuel solenoid relay 86 andbreaker open/close relay 88. Control mode is switched to "cool-down" ifeither breaker 58 is opened, or synchronization is lost for someexternal reason. Control mode is switched to "unloading" if a remote orlocal stop signal is received.

In the "unloading" mode (box 314), microcomputer 80 turns on fuelsolenoid relay 86 and breaker open/close relay 88. One minute maximum isallowed for load to transfer to another generator, then control isswitched to the "cool-down" mode. Control mode is also switched to"cool-down" if a remote or local stop signal is received. Control modeis switched back to "on-line" if a remote or local start signal isreceived.

Referring now to FIG. 15, in the "cool-down" mode (box 316),microcomputer 80 turns on only fuel solenoid relay 86. After a presettime in the cool-down mode has elapsed, control is switched to the"ready" mode. Otherwise, the control mode is switched to"coming-up-to-speed" if a local or remote start signal is received.

As discussed above, several types of microcomputer controlled voltageregulator circuits have been described in the prior art and may beuseful in a controller 64 in accordance with the present invention. Thevoltage regulation scheme of controller 64, however, differs from priorart voltage regulation schemes in the manner in which voltage signalsare sampled and processed for increased accuracy, and also in the schemeby which a voltage control signal is generated from those sampledvalues. This scheme or code routine is discussed below with reference toFIGS. 16 and 17.

The routine incorporates error signal integration steps which allowsmall errors to be detected and compensated for, while limitinginaccuracy due to noise. The routine also provides that the voltageregulator does not attempt to correct a detected error in one step, butcorrects the error gradually or fractionally, i.e., corrects less thanthe entire error in each step. This is effective in essentiallyeliminating overcorrection and the consequent possibility of oscillationof generator voltage about a preset value.

It should be noted here that for computation purposes nominal generatorvoltage is arbitrarily set at a value 36,000 by multipying whatever thenominal voltage really is by an appropriate value. This provides thateven the smallest errors detected may be treated as integer values forcomputation purposes.

Referring first to FIG. 16, the change in alternator voltage since thelast time the routine was executed, a short time previously, iscalculated and stored for later use as a "differential term" (box 320).For a voltage change of 1% per second this term will have a value ofplus or minus twenty-four (±24), depending on whether volatage isincreasing or decreasing. Depending on the current mode of operation ofcontroller 64, one of five sections of code is executed (box 322). Thesecode sections are executed for determining a control or set pointvoltage to which voltage will be controlled. In the "shut-down" mode,there is no voltage regulation and the voltage set point is zero. In the"starting" mode, which is active during cranking and acceleration tospeed, the voltage setpoint is set at seventy-five percent of itseventual value. In an "at-speed" mode, voltage setpoint is quickly andsmoothly increased to one hundred-percent of the "normally operating"setpoint value. This allows for fine corrections. In the "synchronizing"mode, the voltage set point is adjusted to match the voltage of line 36.In the "on-line" mode, the voltage set point is set its "normallyoperating" value, plus any fine adjustment which may be made fromsupervisory control and plus any adjustment required for reactive powerloading, used to prevent regulator conflict over line voltage. Once thesetpoint has been determined in accordance with the operating mode ofcontroller 64, the following instructions are executed in the sequencedescribed.

If the frequency of alternator 59 falls below a set threshold value,voltage starts to decrease in proportion to further reductions infrequency (box 324). This action protects electro-magnetic power devicessuch as transformers that may be connected to the power system. Changesto the voltage setpoint are limited to ten percent per second to avoidsudden alternator voltage changes. The actual alternator voltage issubtracted from the setpoint to obtain the voltage error (box 326), thevoltage error, which will be positive when the actual voltage is too lowand negative when too high, is then processed (boxes 328-346) by a whatmight be termed a proportional, integral, differential control algorithm(PID).

PID algorithm constants referred to in the following explanation arechosen by calculation and experiment to maximize the performance of thevoltage regulator. Note that the differential term value has alreadybeen calculated as discussed above.

First the error is limited to a preset maximum positive or negativeerror if necessary (box 330). The voltage error is then added to anexisting number that represents accumulated error and is referred to asan "integral term" (box 332). The integral term is limited to a presetmaximum positive or negative value, preferably ±20,000, if necessary(box 334). This limitation is usally not applied during normal running,but may be necessary when large voltage errors are present, for example,during a period when a generator is being brought up to speed prior tobeing connected on-line. The voltage error is multiplied by a presetconstant, preferably about 0.3, and the result stored as a "proportionalterm" (box 336).

Continuing now with reference to FIG. 16, the previously calculateddifferential term is also multiplied by a preset constant (box 338). Apreferred value for this constant is about 0.6. The differential term isnext added to the proportional term, the result being designated as a"running value" (box 340). The running value deviates either positive ornegative with the amount of deviation proportional to the error involtage. Since small deviations are more acceptable than larger ones, ifthe running value is less in magnitude than a preset value (PSRV1) ineither the positive or negative direction, the running value is reducedby fifty percent (box 342). If the running value magnitude is more thanPSRV1, it is reduced by a fixed value equal to 50% of PSRV1. If theresultant running value is less in magnitude than preset value PSRV2,the running value is reduced by fifty percent (box 342). If the runningvalue magnitude is more than preset value PSRV2, it is reduced by afixed value equal to 50% of the preset value PSRV2. Fixed reductionvalues are preferably set at 0.25 of gain (or loss) if it is less thanabout ±1% and at about 0.5 percent of voltage gain or loss if it is lessthan about ±0.3%. The action of these two thresholds is to providesmooth transitions in control, without discontinuities, with lessresponse when the error is low, and greater response when the error isgreater. Finally, without altering the integral term value itself, theintegral term value is multiplied by a preset constant multiplier andthe result is added to the last calculated running value (box 344). Therunning value is now the signal RCO made available to voltage regulator82 (see FIG. 5), the higher the running value, the higher the signal AFDdelivered to alternator 59, and the higher the alternator field current.

The above described routine for computing voltage correction signal RCOand hence AFD is executed once for every cycle of power, for example,every one-sixtieth of a second at nominal 60 Hz frequency. Generatorvoltages sampled by the above-described routine are those voltages whichhave been processed by circuits 90 of FIG. 4 and computed and stored bymicrocomputer 80. These voltages are also sampled at a periodicallycalculated interval of exactly 48 times during every cycle of power,i.e., about one millisecond for 60 Hz nominal frequency. Voltageregulator 82 uses the running value or RCO signal at a rate which willeffect corresponding changes in field current at a rate which issynchronized to generator frequency, preferably at every cycle of power.This rate is not fixed, as generator frequency is itself variable withincontrolled preset limits. This scheme of synchronous correction usingasynchronously-sampled, fixed interval, generator-voltage sampling andvoltage-correction signal computation, together with employment oferror-signal integration, and a progressive, fractional error correctionscheme, are believed to provide for greater control accuracy and voltagestability than prior art microcomputer based voltage correctionarrangements.

A similar scheme of error signal integration combined with progressive,fractional error correction is employed for frequency control ofalternator 59. A description of this scheme is set forth below withreference to FIG. 18 and FIG. 19.

Referring first to FIG. 18, microcomputer 80 first decides which speed(frequency) monitoring source to use for computing an error correctionsignal (box 350). Two frequency monitoring signals are available tomicrocomputer 80. One signal is the signal ES see FIG. 4 provided byengine 57 via a magnetic pick up (not shown) and having the form of apulse train. An advantage of this signal is that it is available whetherof not the alternator 59 is producing voltage. The other signal iscomputed by microcomputer 80 using the mathematical inverse of themeasured time between zero-crossings of monitored alternator voltageoutput. This signal is only available during normal running conditions.Microcomputer 80 also computes the line frequency in this manner for usein synchronization routines discussed above. If either alternatorvoltage or magnetic pickup frequency ES are below preset values, themagnetic pickup frequency ES is used (if this pick-up device isconnected). Otherwise the computer-calculated frequency is used.

Next (box 352), Microcomputer 80 executes one of seven setpointdetermining routines depending on the controller operating mode. In the"shut-down" mode there is of, course, no control necessary and thegovernor actuator is shut down. In the "starting" mode, which is usedwhen cranking, waiting between cranks, and coming up to speed,thefrequency control setpoint is set at its full (one-hundred percent)desired value. In the "at-speed" mode, the frequency control setpoint isset at its full value, and fine adjustments are allowed. In the"synchronizing" mode, the frequency setpoint and a relative phasesetpoint are set at the monitored line frequency and phase angle.

In the "on-line" mode, the setpoint is set at its full value, plus anyfine adjustments required by supervisory control or droop adjustmentsfor power loading or unloading. In the "unloading" mode, the setpoint isset at ninety-eight percent of its full value, which forces loadtransfer to other generators. In the "cooling-down" mode, the setpointis set at seventy-five percent of its full value. Any changes in thefrequency set point required by changes in mode as discussed above, orby a remote instruction or request, are limited (box 354) to 0.6 Hertzper second (Hz/sec) to avoid too sudden speed changes of engine 57. Itshould be noted here that as in the case of the above-describe volatgeerror determining scheme nominal frquency is set at an arbitrary highnumber, preferably about 20,000 for computation purposes, whatever thegenerator nominal frequency actually is.

The frequency set point is subtracted from the monitored frequency todetermine the frequency error, which may be positive or negative (box356). The frequency error is added to an existing number that representsaccumulated frequency error, and is referred to as an "integral term"(box 358). The integral term is limited to a preset maximum value andminimum values, if necessary (box 360). The frequency error is thenmultiplied by a constant multiplier, preferably about 0.3, and theresult stored as a "proportional term" (box 362).

Continuing now with reference to FIG. 18, without affecting the integralterm itself, the integral term is multiplied by a constant multiplier,preferably about 3.0, and the result is added to the proportional termresulting in a "running value") (box 364). Monitored actuator currentACI is added to the running value (box 366). The differential speed termis calculated by calculating the change in speed since the calculationwas done the last previous time. For a 1% per second frequency changethis value will be about 2.3. The differential term is multiplied by aconstant multiplier, preferably 3.0 and added to the running vale (box368). The resulting running value ACO is now made available to governorcontroller 84 as a correction signal for setting the actuator current(box 370).

As discussed above an important feature of a controller 64 is thatmicrocomputer 80 therein is self reprogrammable. By self reprogammableit is meant that the computer may be remotely provided with requiredmodifications to its existing program from central computer 40, and canimplement these modifications with only momentary loss of control ofsome other essential functions of controller 64. One preferred schemefor effecting such a program modification is set forth below.

When reprogramming a computer of a controller is desired, a command issent from central computer 40 via telecommunications link 39 to thesupervisory controller 64, the command indicating which controller'sprogram is to be modified. The supervisory controller instructs thatcontroller to shut down the generator with which it associated and,thereafter, to switch its control mode to a "modify" mode.

In the "modify" mode, NVRAM 106 (see FIG. 6) is first partially erased,and then programming instructions from EPROM 108 are transferred(copied) to NVRAM 106. These transferred programming instructions,including the reprogramming elements here described, continue to be usedby microcomputer 80 for operating controller 64. The copy of theinstructions is then modified in accordance with instructionstransmitted from central computer 40 directly. Once the modificationsare complete, the modified copy of the instructions is transferred byprocessor 100 to EPROM 108. Operation of the computer then proceeds inaccordance with the modified instructions stored in EPROM 108, NVRAM iserased to delete the originally transferred instructions, and NVRAM 106then receives control parameters from the supervisory controller and isready to begin storage and logging of designated operational variables.

An advantage of the above described reprogramming method is that it isnot necessary to transmit a complete set of programming instructionswhen all that may be required is to make minor changes for example tooperating priorities. An operator in central computer 40 has terminalaccess to the copied instructions in NVRAM 106 as though original codewere being modified and may modify that code by keyboard instructions inthe usual manner of code editing.

Setpoint and all operating parameters and variable may be adjustedwithout changing the program itself. If the proper operation is lostaccidentally during parameter changes, correct operation may be restoredby performing a "factory default reset" from central computer 40. Thisreestablishes a set of standard setpoint and parameter values.

Throughout the foregoing detailed description of the present invention,reference has been made to central computer 40. Central computer 40 ispreferably located in a central management station operated by an entityresponsible for managing and servicing generating stations 32. Centralcomputer 40 is preferably programmed, at a minimum level, to transmit toand receive from the current supervisory controller 64 in each of thegenerating stations, technical maintenance packages of data. Thesepackages may include instructions for switching a controller to the"modify" mode as discussed above for modifying a computer program;instructions to reset or re-initialize a computer; and instructions torestore a set of default variables or setpoints after these have beenmodified. Central computer 40 receives alarm notifications fromsupervisory controllers, and has access to all of the contents of theinternal memories in any microcomputer 80 in a controller 64. Centralcomputer 40 can thus access all of the logged variables for observingefficiency trends, electrical use patterns and the like. Where, asdescribed above, a microcomputer 80 has only sufficient memory to log aselected group of all of the possible variables monitored or computed bya microcomputer 80, the group to be logged can be selected and changedby central computer 40.

In one preferred configuration, computer 40 is programmed to displaylogged data in a form which can be analyzed by a person operating thecomputer. In FIG. 19 is depicted one preferred form of a display 380 asit would appear on a cathode ray tube (CRT) monitor screen of centralcomputer 40. Display 380 depicts (curve 382) a generator's efficiency inKWH per gallon over a twenty four hour time period. Generator variablesother than efficiency may be displayed by selecting the desired variablefrom a menu 384.

It will be evident to those skilled in the art to which the presentinvention pertains that computer 40 may be programmed to analyze trendsin logged data and provide performance predictions from such analysis.Those skilled in the art may devise such analysis routines withoutdeparting from the spirit and scope of the present invention. Further,those skilled in the art will recognize that the number of variableswhich may be logged by a generator controller 64 and the number ofcontrol functions of a controller 64 are not limited to those describedin the above-discussed embodiment of the present invention. The numberof logged variables and the number of functions controlled may beincreased by increasing memory size, processor speed, and data buscapacity in microcomputer 80 of the controller without departing fromthe above described operational principles and features of thecontroller, which are an important aspect of the present invention.Useful in particular would be to provide for automatic or remotelycommanded engine control and adjustment functions, for example injectortiming. Adding such functions could further reduce the necessity forhuman intervention in a generating station autonomously controlled inaccordance with the present invention.

In summary, a control system and circuits for distributed electricalpower generating stations has been described. Each generating stationincludes a plurality of generators, which together provide power for auser group or community.

Each of the generators includes a computer based controller, thecontrollers being in electronic communication with each other forcooperatively and autonomously controlling the generator group. Anarbitrarily determined one of the controllers assumes a supervisory rolein directing the operations of the other controllers at any instant,while the non-supervisory controllers merely monitor the generators withwhich they are associated. The supervisory controller is in electroniccommunication with a central computer for reporting performance datathereto and receiving operating instructions therefrom. Should asupervisory controller relinquish the supervisory role for any reason,another controller assumes the supervisory role in a time periodsufficiently short that automatic cooperative control of the generatorsproceeds essentially uninterrupted.

Also described above are novel electronic circuits for providingimproved measurements of parameters used for voltage control, frequencycontrol and fuel flow measurement. These circuits, together with novelasynchronous sampling and correction methods of processing the measuredparameters and effecting corrections based thereon, are believed toprovide greater control accuracy and stability than prior artarrangements for providing such control and measurement.

The system and circuits of the present invention have been described anddepicted in terms of preferred and other embodiments. The invention isnot limited, however, to the embodiments described and depicted. Rather,the invention is defined by the claims appended hereto.

What is claimed is:
 1. In an engine driven electrical power generatorarrangement, a method for determining fuel efficiency of electricalenergy generation, comprising the steps of:(a) from a magnetic rotaryvane flowmeter providing first and second current pulse signalsrepresenting respectively fuel flow to and fuel flow from the engine,said current pulse signals having a frequency representative of volumefuel flow, and having a magnitude representative of fuel temperature;(b) converting said first and second current pulse signals to first andsecond voltage pulse signals; (c) determining from said first and secondvoltage pulse signals respectively first and second values of fuelvolume flow and first and second values of fuel temperature; (d) fromsaid first and second values of fuel volume flow, said first and secondvalues of fuel temperature and from a predetermined standardtemperature, standardizing said first and second fuel volume flows to adensity corresponding to said standard temperature; and (e) subtractingsaid standardized second fuel volume flow from said first standardizedfuel volume flow thereby determining a fuel consumption value; (f)receiving a signal from the generator that the generator has generated apredetermined amount of electrical energy; and (g) calculating the fuelefficiency of electrical energy generation from the fuel consumptionvalue and the predetermined amount of electrical energy.
 2. The methodof claim 1, wherein any one of said fuel volume flow rates is determinedby the steps of (h) recording a highest and a lowest value of saidvoltage pulses (i) averaging said highest and lowest values of saidvoltage pulses thereby providing an average voltage value (j) counting afrequency with which said voltage pulses cross said average voltagevalue, and (k) determining said fuel volume flow from said frequency. 3.The method of claim 2, wherein any one of said first and second fueltemperatures is determined by the step of (l) subtracting said lowestrecorded voltage value from said highest recorded voltage value.